1. Field of the Invention
The invention relates to techniques for removing corrugations from the ends of helically corrugated pipe and to products produced by such techniques.
2. Description of the Prior Art
Corrugated pipe is used in a wide variety of applications such as conduits for conveying water, piles for supporting buildings, and so forth. In particular, helically corrugated pipe often is preferred because it is stronger than annularly corrugated pipe. As used here, helically corrugated pipe refers to an elongate, tubular member having corrugations helically disposed with respect to a longitudinal axis of the member; annularly corrugated pipe refers to such a member having corrugations lying in a plane perpendicular to a longitudinal axis of the member.
Frequently, it is desirable to join sections of corrugated pipe end-to-end to form an elongated conduit or other structure. One technique for forming an elongated conduit is to join the sections telescopically so that an end of one pipe is nested within an end of another pipe. Accordingly, by making the ends of a given pipe section of slightly different diameters, this joining process can be used to connect any number of pipe sections. A significant advantage of the telescopic method of joining pipe sections is that specially configured connectors generally are not needed or are greatly simplified, and the pipe sections can be sealed and secured with a minimum of sealant and fasteners.
It is apparent that the ends of the pipe sections must be modified from their originally corrugated form if the pipe sections are to be joined telescopically. Although it is known to provide annularly corrugated pipe sections having straight end portions of different diameters, there presently is no known technique (other than this invention) for straightening the ends of helically corrugated pipe to produce straight ends which can be telescoped together.
Various attempts have been made to produce acceptable helical pipe connections, but it is believed that none have been entirely satisfactory. For example, it is known to rotate the ends of helically corrugated pipe between rollers to provide a plurality of annular corrugations at each end, and then to couple ends of successive pipe sections by means of a ring connector joining the abutting, annularly corrugated end portions. Although pipe sections joined by this technique are strong enough and seal satisfactorily, separate connectors must be procured and this increases the expense of the assembly.
Another proposed technique involves rolling the ends of helically corrugated sheet metal ducts between knurled rollers to produce at one end a straightened, knurled end portion, and at the other end a knurled end portion which subsequently is tapered by a crimping operation. This technique may be acceptable for joining sheet metal ducts (about 22-28 gage) especially if they are, as much ducting now is, aluminum. The technique is unacceptable for joining corrugated steel pipe (about 8-16 gage) because, among other reasons, such relatively thick steel is not susceptible to crimping.
Yet another proposed technique involves deforming an end of helically corrugated ducting between rollers to produce a tapered end portion having square-form threads. The modified end portion can be screwed directly into the unmodified end of another duct section. Although it is believed that this technique might function effectively to join aluminum sheet metal ducts, it is believed inacceptable for heavier-gage steel material because, among other reasons, such threads could not be found effectively.
In both approaches in which a tapered end portion is formed, it is difficult to maintain the orientation between the duct and the rollers during the rolling operation, with the result that the reworked end portion may not have an accurately controlled diameter. Consequently, it may be difficult to seal connected duct sections, and the modified end of the duct could be weaker in certain places than desired.